1. Field of the Invention
The present invention relates to an objective lens for an optical pickup apparatus used to record and reproduce information on and from an optical recording medium by radiating a light beam, such as a laser beam, onto the optical recording medium, and to the optical pickup apparatus using the objective lens, and further to an information recording/reproducing apparatus.
2. Description of Related Art
There is an information recording/reproducing apparatus that records and/or reproduces, by optical means, information on and/or from an optical recording medium such as a CD (Compact Disk) or a DVD (Digital Versatile Disk). The information is read and/or written from and/or to the optical recording medium by radiating light onto the optical recording medium and detecting the intensity or the like of the reflected light therefrom.
There is a growing need for ever larger recording capacities of optical recording media. One solution to meet this need would be to shorten light source wavelengths for reading and/or writing information on the optical recording medium. For example, a DVD-formatted, 12 cm optical recording medium typically uses a 650 nm read/write laser beam. When the wavelength of the laser beam is shortened to 405 nm, and if optical systems exhibiting the same condensing performance as that at 650 nm are used, the recording capacity can be increased by a factor of substantially 2.6.
However, a shorter recording/reproducing wavelength of 405 nm would not be compatible with a DVD-compliant recording/reproducing wavelength of 650 nm. Furthermore, in a DVD recording/reproducing apparatus, its optical systems are usually modified so as to, for example, reproduce information from CD media. Thus, compatibility with existing CDs would also have to be considered.
Another solution would be to ensure compatibility with such conventional media (DVDs or the like) using optical systems suitable for a plurality of wavelengths (e.g., 650 nm and 405 nm). If as many optical systems (e.g., objective lenses) as the plurality of wavelengths are mounted, such another solution would be feasible. However, this solution would also involve an increased number of parts, a further complication of tracking and focus servo mechanisms, or the like, which would further elevate the manufacturing cost of the information recording/reproducing apparatus disadvantageously.